Method for treatment of wood

ABSTRACT

A method for treatment of one or more wood elements by pressurization comprises the steps embedding the wood elements into a pressure medium, of increasing the pressure in the pressure medium, whereby the wood element is compressed by transmitting the pressure via the pressure medium to the wood elements, and of reducing the pressure in the pressure medium, whereby the wood element is relieved. During the treatment, liquid present in the wood elements is driven out therefrom. The pressure medium comprises a plurality of solid bodies with intermediate spaces. The solid bodies transmit the pressure to the wood elements such that a pressure difference arises between the wood elements and said spaces, which pressure difference drives out the liquid. During the relief phase, the wood elements substantially resume their original shape. The method can also be used for introducing impregnating liquid into the wood elements after the liquid expulsion.

TECHNICAL FIELD

The present invention relates to a method for treatment of one or morewood elements by isostatic pressurization, the wood element being placedin a bed of a pressure medium and the pressure medium being pressurized,the pressure medium thus transmitting the pressure to the wood element.

The method is well suited for drying of wood with a high moisturecontent. The method is particularly well suited for drying with asubsequent impregnation of kinds of wood which are otherwise difficultto impregnate, for example spruce.

BACKGROUND ART AND PROBLEMS

It is previously known to change the properties of wood products bypressure treatment. Pressure treatment has been used, for example, forcompressing and hardening of wood. In this connection, particularly goodresults have been obtained by treatment by means of isostaticpressurization of the wood elements. In a previously known method, thewood elements to be treated are placed surrounded by a pressure mediumin a compression chamber. The pressure medium consists of a plurality ofadapted rubber elements, shaped, for example, as balls, elongated stripsor cubes. The pressure medium is delimited in the pressure chamber froma working fluid, for example hydraulic oil, by an elastic membrane. Bypressurizing the working fluid by means of a hydraulic pump, theworked-up pressure is transmitted to the pressure medium. The pressuremedium forms around the wood elements and brings about a uniformcompression thereof. This results in a permanent compression andhardening of the wood elements.

A disadvantage with the prior art is that the liquid and moisturecontents of the wood elements prior to the pressure treatment must bereduced to a level acceptable for the pressure treatment. The reasontherefor is that the incompressible liquid during the pressurization iscontained in the wood element, whereby compression of the wood elementis not possible. Thus, it has not been possible to pressure-treatfreshly sawn timber or other wood products with too high a moistureratio.

A closely related problem is that, with the previously known technique,it has not been possible to utilize pressure treatment for the verypurpose of drying of wood elements. To reduce the moisture ratio of woodproducts, it has hitherto been necessary to use the traditional methods,which are based on heating and/or air drying by means of fans. Thesemethods, however, are relatively time-consuming and therefore cause highcosts.

Another, and perhaps even more serious problem, which is a consequenceof the traditional drying methods, concerns the subsequent impregnationof the dried wood products. This often entails serious problems, sinceit is difficult to cause the impregnating agent to penetratesufficiently deep into the wood. Impregnation of wood products, such assawn timber, is often desirable. The impregnation aims at increasing theresistance of the wood products to certain processes, such as bacterialor fungus attack, causing degradation in the wood. Usually, thepreserving agent is dissolved in a liquid, which by means of variousmethods is brought to penetrate into the wood. The penetration may beachieved, for example, by soaking the wood products or by driving in theimpregnating liquid by means of an over-pressure. In the latter case,the impregnation is usually preceded by vacuum treatment of the woodproducts.

The penetration of the liquid into the wood may take place either bydiffusion or flow. In the case of diffusion, the liquid penetrates veryslowly into the wood by means of the concentration of the impregnatingsolution. In the case of penetration by flow, on the other hand, theliquid may quite rapidly penetrate into the wood by utilizing the fibresand pores occurring in the wood. During impregnation, flow penetrationis preferable to diffusion penetration owing to the higher rate ofpenetration.

In coniferous wood, more than 90% of the wood consists of wood fibre,so-called tracheids. In the live tree, the purpose thereof is, amongother things, to conduct liquid. The tracheids consist of about 3millimetres long, elongated hollow fibres. They are arranged essentiallyparallel to the longitudinal direction of the tree and each other andare mutually axially displaced. Liquid may be transported from onetracheid to an adjacent one via so-called pores. The pores, which may beof different kind, for example ring pores or simple pores, constituteopenings in the tracheid wall. The pores usually comprise some type ofclosing member, a so-called pore membrane. Because the pore membranesopen and close the pores, liquid is allowed and prevented, respectively,from passing from one tracheid to another.

During impregnation of sawn timber, the liquid penetrates very rapidlyfrom the end surfaces of the wood elements. The longitudinal tracheidsare cut off there and the liquid enters easily. To allow the liquid topass into the wood, from one tracheid to another, the pores must beopen. Sooner or later the liquid encounters a tracheid where all thepores are closed and the penetration thus stops.

It has proved that traditional drying of coniferous wood causes closingof the pores. When the wood dries, the pore membrane is displaced from acentral position and closes the pore opening. What causes the membraneto move are capillary forces in the water which is dried away. When themembrane has clogged the pore opening, it is impossible to move themembrane even if the wood is subjected to very high pressure. This isprobably due to the membrane adhering to the pore wall and to the factthat a bond in the form of hydrogen bridges arises therebetween.

The above reasoning is an explanation why, after traditional drying ofsoftwood, it is so difficult to cause impregnating liquid to penetratesufficiently deeply into the wood. Further, it has been known for a longtime that it is considerably more difficult to impregnate spruce thanpine. This is due, among other things, to the fact that a larger numberof pores close during drying of spruce than of pine, and to pine havingfewer and smaller pores.

A special problem with previously known drying methods is thus that theyrender the subsequent impregnation of the wood considerably moredifficult. This is particularly true of certain kinds of wood, such asspruce.

The object of the present invention is to provide a method for treatmentof wood which allows pressure treatment to be used for the drying of thewood and which makes possible a considerably simplified impregnation ofthe dried wood.

THE SOLUTION

The above-mentioned object is achieved according to the invention with amethod of the kind mentioned in the introductory part of the descriptionand which is characterized in that the wood element (4) contains liquid,which during the compression is driven out by the fact that the pressuremedium comprises a plurality of solid bodies (8 a) with intermediatespaces (8 b), whereby the solid bodies transmit the pressure to the woodelement such that a pressure difference arises between the wood elementand the mentioned spaces when the pressure medium is pressurized, whichpressure difference drives the liquid from the wood element to thespaces, and that the wood element, during the pressure relief, isexpanded substantially to its original shape.

Since the pressure medium comprises solid bodies, it is ensured that thespaces between the bodies are maintained also during the pressurizationof the pressure medium. This makes possible the pressure difference,which is necessary for driving out the liquid, during the compression ofthe wood element. The method according to the invention thus allows woodelements to be dried by means of pressure treatment. Such pressurizeddrying is significantly faster than the prior art drying methods. Dryingof freshly sawn timber to a moisture ratio of about 30%, whichpreviously, for example in a drying furnace, took up to 24 hours, can becarried out in less than 2 minutes with the method according to theinvention.

The raised pressure which is obtained during the compression phase maybe maintained in the pressure medium and in the wood element during acertain predetermined holding time prior to the beginning of thepressure relief phase. In this way, it is ensured that the desiredquantity of the liquid has time to penetrate out of the wood element.

The solid bodies included in the pressure medium may consist of a largenumber of different materials and they may have different hardnessdepending on under what maximum pressures they are to be used. Somematerials which have proved to be particularly suitable are polymers,sand, glass, stainless steel, bronze and aluminium oxide. In thoseapplications of the method where only lower pressures are utilized, thesolid bodies may have a hardness according to the international IRHscale of IRH shore A 95° or more. If higher pressures are used, thehardness should preferably exceed IRH shore D 80°. In this connection itshould be noted that the IRH shore D scale represents a higher hardnessinterval than the IRH shore A scale.

Further, the solid bodies may have an infinite number of geometricalshapes. They may be completely asymmetrical and mutually different,which is the case, for example, with grains of sand, but they may alsobe symmetrical and identical, for example as steel balls. The size ofthe solid bodies is of importance to the result. Too large bodies causevisible impressions in the surface of the wood element, whereas toosmall bodies or grains make the escape and removal of liquid between thespaces and from the wood element difficult. Attempts have shown thatsolid bodies with a diameter or mesh size smaller than 10 mm aresuitable. Particularly favourable results are obtained if the grain sizeis between 0.1 and 5 mm.

The fact that the wood elements during the relief phase restore theiroriginal shape in this context means several advantages. For one thing,in many respects, the same properties as traditionally dried wood areimparted to the wood elements. For example, wood dried according to theinvention exhibits no difference from other wood, from the strengthpoint of view or any other structural engineering point of view, whichmakes it possible to use it as ordinary wood without further adaptation.Further, the expansion of the wood element during the relief phasecontributes to make possible a significantly simpler impregnation of thewood element.

In use of the method, during the compression, a considerable proportionof pore membranes present in the wood element may be caused to leavetheir pores. The pore membranes are flushed away with the aid of therelatively fast flowing liquid, which was present in the wood elementfrom the beginning and which is pressed out during the compression. Asis clear from the above, the pore membranes constitute one of the mostserious reasons for traditionally dried wood being so difficult toimpregnate. As a considerable proportion of the pore membranes accordingto the invention are removed from the pores, a significant proportion ofthe tracheids will, after pressurization, lie open to the impregnatingliquid. In this way, the resistance to impregnation by means of aflowing liquid is considerably reduced. The impregnating liquid cantherefore, in a simpler and faster manner, penetrate considerably deeperinto the wood than what was previously possible. The method according tothis embodiment makes possible an impregnating efficiency which has notbeen possible at all in the past.

Further, the rate of pressure increase and the maximum pressure may beadjusted to control the proportion of pore membranes which are caused toleave their pores. This control makes possible, for example, removal ofan optimum proportion of pore membranes without damaging the wood inother respects. The maximum pressure as well as the rate of pressureincrease are chosen depending of the kind of wood and the dimension ofthe wood. Attempts have shown that pressures of between 400 and 1500 barare often suitable. Particularly favourable results have been achievedat between 700 and 1100 bar.

Still more important for obtaining a well-balanced blow-out or flushingaway of pore membranes is the rate at which the pressure in the pressuremedium and the wood element is increased. The faster the pressureincrease, the higher the liquid flow and the larger the proportion ofremoved pore membranes. Too rapid pressure increase, however, may damagethe tracheids and other wood components. During tests, rates of pressureincrease of between, on average, 2 and 40 bar/second, preferably between10 and 25 bar/second have proved to be suitable.

According to one embodiment of the invention, an impregnating liquid maybe allowed into the wood element during the relief. This offers a methodof treatment for drying and impregnation which is considerably fasterand more efficient than prior art methods. Drying and impregnation,which according to the prior art take from several hours up to severaldays, are carried out in just a few minutes using the method accordingto the invention. If a sufficiently large proportion of pore membranesare removed during the liquid expulsion, the embodiment also entails aconsiderably larger impregnation depth and a higher impregnationefficiency than what has been possible so far.

Further, the impregnating liquid may be supplied to the spaces in thepressure medium when the pressure medium is pressurized. Theimpregnation according to this embodiment takes place by driving theimpregnating liquid, during the relief of the wood element, into thewood element by means of the pressure difference which arises betweenthe spaces and the wood element during expansion thereof. In this way, asimple and efficient treatment cycle is obtained without interruption orreloading. In addition, the energy which is used for building up theliquid expulsion pressurization is utilized also for the impregnation.This renders the process considerably more effective in relation to theprior art, where the drying energy cannot be used in any way during thepressure impregnation.

BRIEF DESCRIPTION OF THE DRAWING

Exemplifying embodiments of the method according to the invention willbe described below with reference to the accompanying drawings.

FIG. 1 is a schematic cross section through a press for carrying out themethod according to the invention.

FIG. 2 is a schematic longitudinal section, greatly amplified, throughpart of a wood element when, embedded into a pressure medium, itundergoes a treatment according to the invention.

The press shown in FIG. 1 comprises a pressure chamber 1, which isdefined by an upper 2 and a lower 3 part. By separating the two parts 2and 3, the pressure chamber is opened, thus providing a possibility ofinserting and withdrawing the wood elements 4 which are being treated.In the pressure chamber 1 an elastic diaphragm 5 is arranged. Thediaphragm 5 is attached to the upper part 2 such that it is fixedbetween the upper part 2 and the lower part 3 when the pressure chamber1 is closed and such that the lower part of the pressure chamber isexposed when the chamber is opened. When the pressure chamber 1 isclosed, the diaphragm 5 delimits one primary 1 a and one secondary 1 bcompartment. The primary compartment la of the pressure chambercommunicates, via a channel 6, with a hydraulic unit 7 in the form of ahigh-pressure pump.

Further, in the secondary compartment 1 b of the pressure chamber 1, twoelongated wood elements 4 are arranged. These are embedded into apressure medium 8, which completely surrounds the wood elements 4. Apressure vessel 9 for storage and pressurization of impregnating liquid,is placed outside the press and communicates, via an impregnation valve10, with distribution conduits 11, arranged in the pressure medium, inthe vicinity of the wood elements. The pressure vessel 9 is alsoconnected to a pump (not shown) for pressurization of the impregnatingliquid. The distribution conduits 11 are provided with small spray holes(not shown) and extend on two sides of each wood element alongessentially the whole length of the element. Likewise, in the secondarycompartment 1 b and in the vicinity of the wood elements 4, severaldraining pipes 12 (only one being shown) are arranged. The drainingpipes 12 are provided with openings (not shown) and communicate via adrain valve 13 with the outside of the press. Both the impregnationvalve 10 and the drain valve 13 may be controlled to open and close fromthe outside of the press.

The part of a longitudinal section of a wood element 4, schematicallyshown in FIG. 2, comprises a number of elongated tracheids 14. Eachtracheid comprises walls 15, an inner void 16 and openings 17 in thewalls. At two of the openings, or the pores 17, a pore membrane 18 isdisposed. To the left in the figure it is indicated that several of thetracheids nearest the end of the wood element are cut and have no endwall. The wood element 4 is surrounded, on the two sides shown, by thepressure medium 8. This comprises a plurality of glass balls 8 a withintermediate free spaces 8 b. The diameter of the glass balls is around1 mm.

It is described below how two wood elements 4 are treated according toone exemplifying method according to the invention. When the upper part2 of the pressure chamber 1 is removed, the wood elements 4 are liftedinto the lower part of the pressure chamber 1. The wood elements 4consist of planks of sapwood from spruce and have a moisture ratioexceeding 30%. Normally, the moisture ratio for freshly sawn sapwood ofspruce is between 100 and 150%. The moisture ratio may, of course, varydepending on the kind of wood and the preceding treatment, but generallythe moisture ratio before the treatment should not be too low. Themoisture ratio, which is reduced during the liquid expulsion, influencesthe rigidity of wood. Too low a moisture content causes the wood tobecome more rigid, which counteracts the resumption of the originalshape by the wood elements during the relief. Too low a moisture ratiomay thus entail a lasting compression and hardening of the wood elementswhich is not desirable in this connection.

The wood elements 4 are placed on a bed of glass balls 8 a, whereuponglass balls are poured over them so that they are surrounded by theseglass balls on all the sides. Also the distribution pipes 11 arearranged in the bed, so that the spray holes become evenly distributedalong the wood elements 4 and at an appropriate distance therefrom.Under the wood elements the draining pipes 12 are arranged, with theopenings for draining the spaces 8 b in the pressure medium 8. Thedraining pipes 12 may possibly be arranged such that a majority of theopenings are concentrated in the vicinity of those locations of the woodelements 4 which, during the compression, give off more liquid, forexample the short sides of the wood elements.

When the pressure medium bed is arranged, the pressure chamber 1 issealed by lifting the upper part 2 with the diaphragm 5 onto the lowerpart 3 and securing it thereto. Thereafter, the hydraulic unit 7 isstarted, whereby hydraulic oil is pumped via the channel 6 into theprimary compartment 1 a of the pressure chamber 1. When the primarycompartment is filled with hydraulic oil, the pressure is increased bypumping in additional oil. The raised pressure is transmitted via thediaphragm 5 and the pressure medium 8 in the secondary compartment 1 bto the wood elements 4. Since the friction between the glass balls 8 ais relatively low, an isostatic pressure arises in the secondarycompartment. At the same time, the spaces between the balls areretained. The pressure which is transmitted via the diaphragm causes anequilibrium of forces between all the balls which are in mechanicalcontact with each other. In this way, the pressure is transmittedisostatically from the diaphragm via the balls to all the surfaces ofthe wood element 4. The gas pressure in the spaces 8 b between the balls8 a is not changed to any significant degree during thepressure-increase phase. The atmospheric pressure which prevails priorto the start of the hydraulic unit 7 is retained in all essentialsduring the compression phase.

When the glass balls 8 a now press on the surfaces of the wood elements4, the same high pressure arises in the wood elements 4 as in thepressure medium 8. In this way, liquid, which exists freely in the voids16 of the tracheids 15, is pressurized to this high pressure. A pressuredifference thus arises between the liquid in the wood elements 4 and thespaces 8 b between the balls 8 a in the pressure medium 8. Thisdifference in pressure drives liquid to move from the wood element 4 tothe spaces 8 b in the pressure medium 8. The liquid primarily leaves thewood elements through the possible outlets which cause the lowest flowresistance. Thus part of the liquid passes out through tracheids 14which are cut off at the end of the wood elements. Part of the liquidflows out via pores 17 at the surface of the wood elements and part ofthe liquid diffuses out through the tracheid walls 15. During its flowfrom the interior of the wood elements to the surfaces thereof, liquidtears off pore membranes 18 from the tracheid walls 15 at the pores 17.The torn-off pore membranes 18 are carried with the liquid from tracheid14 to tracheid and thus follow the liquid out of the wood elements 4.

During the pressurization, the drain valve 13 is open. Part of theliquid which leaves the wood elements 4 is transpored via the spaces 8 baway from the wood elements and is collected by the draining pipes 12with their draining openings. The drained-off liquid is passed via thedraining pipes 12 and the valve 13 away from the pressure chamber 1. Thedraining of the spaces 8 b may possibly be accelerated by vacuum suctionof the spaces 8 b with the aid of the vacuum pump (not shown), which maybe connected to the drain valve 13.

To obtain a good result when driving off liquid and pore membranesduring the compression phase, the pressurization rate and the maximumpressure are chosen to suit the wood elements in question. Duringtreatment of sapwood from spruce with an initial moisture ratioexceeding 100%, the pressure is raised from atmospheric pressure byabout 5 bar/second to about 900 bar. The pressurization parameters arealso chosen in dependence on the available pressure medium. Thus, forexample, balls of steel or aluminium oxide withstand pressures exceeding100 bar, whereas solid bodies of, for example, polymers are not used forpressures exceeding about 500 bar.

The high pressure which is achieved during the pressurization phase isnow maintained during a certain predetermined time. This is done inorder to give the desired quantity of liquid ample time to penetrate outfrom the wood elements. The duration of the holding time varies fromcase to case and is determined on the basis of, among other things, thekind of wood, the moisture ratio as well as the rate of pressureincrease and the maximum pressure. By choosing a longer holding time, itmay be possible to allow the rate of pressure increase and the maximumpressure to be lower. This results in a treatment which, admittedly, issomewhat slower but which is also more lenient to the fibre structure inthe wood.

Before or during the compression phase and the holding time, theimpregnating liquid in the pressure vessel 9 has been pressurized to apressure which is considerably higher than the pressure which prevailsin the pressure medium 8 and the wood elements 4. When the compressionphase and the holding time are completed, the drain valve 13 is closed.Thereafter the impregnating valve 10 is opened. The pressurizedimpregnating liquid thus flows out through the distribution tubes 11 andis distributed via the spray nozzles out into the spaces 8 b near thewood elements 4. Since the pressure of the impregnating liquid in thespaces 8 b is now higher than the pressure in the wood elements, theimpregnating liquid penetrates into these. To ensure that a sufficientquantity of impregnating liquid penetrates sufficiently deep into thewood, the pressure difference between the impregnating liquid in thespaces and the wood elements is maintained for a certain holding time.When this holding time is completed, the secondary compartment 1 b isrelieved by evacuating hydraulic oil from the primary compartment.During the relief phase, the wood elements 4 again expand into theiroriginal shape. This leads to an additional pressure difference betweenthe interior of the wood elements and the spaces 8 b filled withimpregnating liquid. This pressure difference now drives additionalimpregnating liquid into the wood elements. Since a considerable part ofthe pore membranes is flushed away, impregnating liquid may penetratefar into the wood elements without difficulty. Only a relatively smallpressure difference is necessary to obtain a satisfactory impregnation,where liquid penetrates into the centre of the wood elements. The reliefcan be carried out relatively rapidly, whereby the pressure can bereduced by about 20-50 bar/second.

After completed relief, when the pressure in the primary 1 a andsecondary 1 b compartments and in the wood element again is around 1bar, the upper part 2 of the pressure chamber is removed, whereupon thewood elements can be removed.

During the impregnation, the moisture ratio of the wood again rises.Normal values of the moisture ratio, both during traditionalimpregnation and the method described above, are around 35-125%. If animpregnated product with a lower moisture ratio is desired, the woodelements may be dried in traditional manner. It is also possible,however, after the active components in the impregnating liquid havereacted with the wood, to dry the wood elements again by means ofpressure treatment. The redundant impregnating liquid thus runs outduring the compression phase, wherafter no liquid is added during therelief phase.

The method described above is only one example of treatment of woodaccording to the invention. The method may be varied in a plurality ofdifferent ways.

For example, wood elements of many other kinds of wood, such as pine,oak, birch, larch, beech, aspen and alder may be treated. In addition tobeing derived from the sapwood, the treated elements may also be derivedfrom the heartwood or constitute a combination thereof.

The treatment is not required to include the impregnation phase, but thewood elements may be relieved without any supply of impregnating liquid.This results in a very fast and effective drying of the wood elements.

The method of supplying impregnating liquid to the spaces when the woodelements are pressurized can be varied in many ways. The impregnatingliquid may, for example, be pumped in via the draining pipes. It is alsopossible, instead of supplying the liquid from an external pressurizedcontainer, to place a flexible container in the pressure medium bed.This flexible container is filled with impregnating liquid before thecompression phase. During the compression phase the liquid is preventedfrom penetrating out into the bed in that the impregnation valve isclosed. The liquid in the flexible container is thus pressurized toessentially the same pressure as that which prevails in the woodelements. When the compression phase with the subsequent holding time iscompleted, the impregnation valve is opened whereby the impregnatingliquid spreads in the spaces of the pressure medium. When the liquid hasspread, the wood elements are relieved whereby they expand to theiroriginal shape. This results in a pressure difference between the spacesand the wood elements which drives the impregnating liquid into the woodelements.

Further, it is not necessary to drain away the liquid which is drivenout of the wood elements during the compression. It is also possible toreuse this liquid by allowing concentrated impregnating liquid, afterthe liquid expulsion, to mix therewith in the bed. Thereafter, theliquid with impregnating agent is returned into the wood elements duringthe relief.

The method of driving out the liquid from the wood element is bestsuited for driving out so-called free water. This is water which, priorto the drying, exists freely in the fibres of the wood and which is notbound in the cell walls of the wood.

What is claimed is:
 1. A method for treatment of one or more woodelements by pressurization, comprising the steps of embedding the woodelement in a pressure medium, increasing the pressure in the pressuremedium, whereby the wood element is compressed by transmitting thepressure via the pressure medium to the wood element, and reducing thepressure in the pressure medium, whereby the wood element is relieved,characterized in that the wood element contains liquid which during thecompression is driven out by the fact that the pressure medium comprisesa plurality of solid bodies with intermediate spaces, the solid bodieshaving a sufficient hardness to maintain the intermediate spaces betweenthe bodies when subjected to pressures over 400 bar, whereby the solidbodies transmit the pressure to the wood element, such that a pressuredifference arises between the wood element and said spaces when thepressure medium is pressurized, which pressure difference drives theliquid from the wood element to the spaces.
 2. A method according toclaim 1, characterized in that the increased pressure obtained duringthe compression is maintained during a predetermined holding time.
 3. Amethod according to claim 1, characterized in that a significantproportion of the pore membranes present in the wood element are broughtto leave their pores.
 4. A method according to claim 3, characterized inthat the rate of pressure increase and the maximum pressure arecontrolled for controlling the proportion of pore membranes which arebrought to leave their pores.
 5. A method according to claim 1,characterized in that an impregnating liquid is introduced into the woodelement.
 6. A method according to claim 5, characterized in that theimpregnating liquid is pressurized and is supplied to the spaces in thepressure medium.
 7. A method according to claim 1, characterized in thatthe pressure medium comprises a granulate, in which the average diameteror mesh size of the solid bodies is smaller than 10 mm.
 8. A methodaccording to claim 1, characterized in that the pressure mediumcomprises solid bodies of polymer material, sand, glass, steel, bronzeor aluminium oxide.
 9. A method according to claim 1, characterized inthat the wood element is pressurized to between 400 and 1500 bar.
 10. Amethod according to claim 1, characterized in that the pressure increasetakes place at a rate of, on average, between 2 and 40 bar/second.
 11. Amethod according to claim 1, characterized in that the hardness of thesolid bodies exceeds IRH shore A 95°.
 12. A method according to claim 1,characterized in that the average diameter or mesh size of the solidbodies is between 0.1 and 5 mm.
 13. A method according to claim 1,characterized in that the wood element is pressurized to between 700 and1100 bar.
 14. A method according to claim 1, characterized in that thepressure increase takes place at a rate of, on average, between 10 and25 bar/second.
 15. A method according to claim 1, characterized in thatthe hardness of the solid bodies exceeds IRH shore D 80°.
 16. A methodaccording to claim 1, further comprising the step of draining the liquiddriven out of the wood element from the spaces.
 17. A method accordingto claim 16, characterized in that an impregnating liquid is introducedinto the wood element.
 18. A method according to claim 17, characterizedin that the impregnating liquid is pressurized and is supplied to thespaces in the pressure medium.
 19. A method for treatment of a woodelement, having a high moisture ratio, exceeding 30%, characterized bythe steps of embedding the wood element in a pressure medium comprisinga plurality of solid bodies with intermediate spaces, pressurizing thepressure medium such that the solid bodies transmit pressure to the woodelement, whereby the wood element is compressed and a pressuredifference arises between the wood element and said spaces, saidpressure difference driving liquid from the wood element to the spaces,during the pressurization draining liquid that has been driven out fromthe wood element, and removing the pressurization, whereby the woodelement is relieved and expands.